Synthesis, structural characterization, and computational study of novel (E)-N′-(1-p-tolylethylidene)furan-2-carbohydrazide

Article abstract of DOI:10.1016/j.molstruc.2013.08.008

An efficient synthesis of the novel (E)-N′-(1-p-tolylethylidene) furan-2-carbohydrazide is described. The molecular structural features were then confirmed by single crystal X-ray diffraction. Quantum chemical calculations including molecular geometry, intermolecular H-bonds, and vibrational frequencies were carried out for the structures to explain stability and geometry using both density functional (DFT/B3LYP) and the Hartree-Fock (HF) with 6-311+G(d,p) basis set. The calculated structural parameters are presented and compared with their experimental X-ray counterparts. The E-isomer is a global minimum on the potential energy surface. However, validation of the computational methods here via comparison with the observed X-ray data enabled computational analysis to predict that head-to-tail E/E-dimer of the observed E-isomer has significantly stronger intermolecular hydrogen bonding compared with the non-observed Z/Z-dimer. It was observed that the stretching mode of NH and CO shifted to lower frequencies, due to pairwise intermolecular NH?O hydrogen bonds. This provides a clear rationale for the isomeric specificity obtained and provides a validation of the optimized method which could be applied to predict structures of other useful carbohydrazides. Generally, it has been concluded that the findings of B3LYP hybrid functional fit better to the observed geometrical and vibrational parameters than the results of the HF.

Full text of DOI:10.1016/j.molstruc.2013.08.008

Journal of Molecular Structure 1051 (2013) 345–353
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structural characterization, and computational study of novel
(E)-N0-(1-p-tolylethylidene)furan-2-carbohydrazide
Rami Y. Morjan a, Ahmed M. Mkadmh b, Fakhr M. Abu-Awwad a, Madeleine Helliwell c, A.M. Awadallah a,
John M. Gardiner d,
⇑
a Chemistry Department, College of Science, Islamic University of Gaza, Gaza, Palestine
b Chemistry Department, College of Applied Science, Al-Aqsa University, Gaza, Palestine
c School of Chemistry, The University of Manchester, Brunswick Street, Manchester M13 9PL, UK
d Manchester Institute of Biotechnology, School of Chemistry, Faculty of EPS, The University of Manchester, Manchester M1 7DN, UK
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
Preparation and solid state study of a novel member of an interesting structural class.
This modeling studies show that the E-isomer is the global minimum isomer.
A rationale for the observed E-selectivity is based on strong E–E dimerization.
a r t i c l e i n f o
a b s t r a c t
An efficient synthesis of the novel (E)-N0-(1-p-tolylethylidene)furan-2-carbohydrazide is described. The
molecular structural features were then confirmed by single crystal X-ray diffraction. Quantum chemical
calculations including molecular geometry, intermolecular H-bonds, and vibrational frequencies were
carried out for the structures to explain stability and geometry using both density functional (DFT/
B3LYP) and the Hartree–Fock (HF) with 6-311+G(d,p) basis set. The calculated structural parameters
are presented and compared with their experimental X-ray counterparts. The E-isomer is a global min-
imum on the potential energy surface. However, validation of the computational methods here via com-
parison with the observed X-ray data enabled computational analysis to predict that head-to-tail E/E-
dimer of the observed E-isomer has significantly stronger intermolecular hydrogen bonding compared
with the non-observed Z/Z-dimer. It was observed that the stretching mode of NAH and C@O shifted
to lower frequencies, due to pairwise intermolecular NAHꢁ ꢁ ꢁO hydrogen bonds. This provides a clear
rationale for the isomeric specificity obtained and provides a validation of the optimized method which
could be applied to predict structures of other useful carbohydrazides. Generally, it has been concluded
that the findings of B3LYP hybrid functional fit better to the observed geometrical and vibrational param-
eters than the results of the HF.
Article history:
Received 6 May 2013
Received in revised form 7 August 2013
Accepted 8 August 2013
Available online 14 August 2013
Keywords:
Hydrazones
Azomethine
B3LYP
Hydrogen bonds
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
the synthesis of a wide range of organic compounds including
1,3,4-oxadiazoles derivatives [4–7]. For example, N-heterocyclic
Hydrazones possessing an azomethine ANHN@CHA proton
represent a key component of organic compounds which have
been used in various biological and chemical applications [1].
These compounds can be synthesized under simple reaction condi-
tions at moderate temperature. These materials are normally gen-
erated via a condensation reaction between an acid hydrazide and
aldehydes or ketones, either in the presence or absence of acid cat-
alyst [2,3]. In addition to their own important properties and appli-
cations, both N-acyl- and N-arylhydrazones are vital precursors for
hydrazones derivatives have received major interest due to their
coordination properties which enable them to act as mono- or
polydentate ligands towards metal ions, and several such metal
complexes have been synthesized and characterized [8]. They also
act as precious spectrofluorimetric reagents in metal ion determi-
nation in various environments including for Os(VIII), Cd(II), Co(II),
and Hg(II) [9]. Furthermore, these compounds may exhibit phar-
macological activities. In fact, there is considerable evidence to
suggest that the hydrazone moiety present in many derivatives im-
parts a valuable pharmacophoric character for example for the
inhibition of COX, treatment of tuberculosis in combination with
⇑
Corresponding author. Tel.: +44 161 306 4530.
E-mail address: gardiner@manchester.ac.uk (J.M. Gardiner).
0022-2860/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2013.08.008

346
R.Y. Morjan et al. / Journal of Molecular Structure 1051 (2013) 345–353
other drugs, and potential inhibitory activity toward protein tyro-
sine phosphate from Mycobacterium Tuberculosis [10–12].
Hydrazones that possess acidic hydrogen are identified by their
prototropic tautomerism. Therefore, two different geometrical
structures are possibly available; syn-Z or anti-E isomers with dif-
ferent tautomeric forms. Inter and Intra- molecular hydrogen
bonds of such compounds and their subsequent influence in gener-
ating different supramolecular arrays have been identified [13–15].
Hydrazone-containing compounds have been attracting sub-
stantial attention in computational sciences. For example, Guner
et al. employed both ab initio and DFT methods to investigate cya-
nobenzaldehyde isonicotinoyl hydrazone [16]. The absorption and
fluorescence energies of substituted aryl-1,8-naphthalimide hydra-
zones was modeled using high level DFT [17]. Also, the structural
activity relationships of a series of pyrrole hydrazones were exam-
ined as new tuberculosis agents where various computed constitu-
tional, topological, physicochemical and quantum–mechanical
descriptors were correlated with their reactivity [18].
calculations were carried out using the SHELXTL package [20].
The non-H atoms were refined anisotropically and H atoms were
included in calculated positions, except for those bonded to N,
which were found by Difference Fourier Methods and refined iso-
tropically. It was necessary to collect the data at 230 K, since flash
freezing to 100 K caused the crystal to break up. The crystal data
are summarized in Table 1.
3. Computational work
The molecular structures of compounds involved in the study
were constructed using Hyperchem 7 [21] and initially optimized
at the Semiempirical PM7 Sparkel level of theory implemented in
MOPAC09 [22]. Then, using Gaussian 09 package [23], the initially
optimized structures were fully optimized at their ground state in
the gaseous phase at the DFT/B3LYP and HF level of theories with
6-311+G(d,p) basis set [24,25]. The stationary natures of the fully
optimized structures were analytically examined by calculating
the harmonic vibrational frequencies at the same level of theories
and then zero point energies were estimated. To generate the cor-
rect frequencies, the computed vibrational frequencies were scaled
by 0.9613 and 0.905 for B3LYP and HF subsequently as reported in
literature [26,27]. Electrical Energies of ground state isomers, di-
mers and rotational states were estimated using single point
In this study, as a part of our ongoing interest in functionalized
hydrazides we report the synthesis of (E)-N0-(1-p-tolylethylid-
ene)furan-2-carbohydrazide and comparison of X-ray structural
characterization with detailed computational investigations of
the structures. In addition, the roles of energy and H-bonding in
the subsequent stabilities of the E/Z-geometrical isomers are com-
putationally investigated.
energy calculations at
a higher level of theory; B3LYP/6-
311++G(2df,pd)//B3LYB/6-311+G(d,p). Predicted energies were
corrected for zero-point vibrational energies. Intermolecular
hydrogen bondings and chemical potentials extrema (maximum
and minimum) were evaluated at the same level of theories. Atom-
ic charges were calculated using natural population analysis [28].
GaussView and Gapedit programs were used for visualization of
structures [29,30].
2. Experimental work
2.1. Syntheses and characterization
FTIR spectra was recorded using Shimadzu 8201 spectropho-
tometer with KBr technique in region 4000–400 cmꢂ1 that was cal-
ibrated by polystyrene. ES–MS and HRMS were recorded on a
Micromass LCT orthogonal acceleration time-of-flight mass spec-
trometer (positive ion mode). 1H NMR spectra were recorded at
400 MHz and 13C NMR spectra at 100 MHz on a DPX400 spectrom-
eter. Chemical shifts are denoted in ppm (d) relative to internal sol-
vent standard.
Furic acid hydrazide (0.0158 mol) and 1-p-tolylethanone
(0.0158 mol) were heated under reflux in ethanol (20 ml) for
30 min until a solid precipitate was formed. The mixture was al-
lowed to cool to room temperature and the solvent removed under
reduced pressure. The solid was washed successively with cold
ethanol, filtered and then recrystallized from cold ethanol to give
Table 1
Crystal data and structure refinement of (E)-N0-(1-p-tolylethylidene)furan-2-
carbohydrazide.
Parameter
Value
C14H14N2O2
Empirical formula
Formula weight
Crystal color
Crystal size (mm3)
Crystal system
Space group
Unit cell dimensions
a (Å)
242.27
Colorless
0.5 ꢃ 0.5 ꢃ 0.5
Triclinic
P ꢂ 1
10.311(7)
11.633(8)
12.480(8)
67.050(12)
74.755(13)
64.172(11)
1232.8(14)
4
the pure product in 89% yield and Mp 169–170 °C. IR (KBr)
m
b (Å)
c (Å)
cmꢂ1: 3178 (NH str.), 1151 (NAN), 1658 (C@O), 1507 (C@C),
1561 (N@C), 1134 (CAO). MS (ESI) m/z: [M+Na)+, 265.0], 1H NMR
(400 MHz, CDCl3) d 10.6 (s, 1H, NH), 7.9 (d, J = 0.9 Hz, 1H, OCHCH,
furan ring), 7.8 (d, J = 7.7 Hz, 2H, aromatic ring), 7.7 (d, J = 8.7 Hz,
2H, aromatic ring), 7.4 (d, J = 3.3 Hz, 1H, OCHCH, furan ring), 6.7
(dd, J = 3.5, 1.7 Hz, 1H, CHCHCH, furan ring), 2.4 (s, 3H, CH3), 2.3
(s, 3H, CH3). 13C NMR (100 MHz, CDCl3) d 162.9 (C@O), 154.3
(C@N), 147.2 (OCHCH, furan ring), 144.3 (OCCH, furan ring),
140.1, 135.0, 129.3, 126.7 (aromatic ring), 115.9 (OCCH, furan ring),
112.6 (OCHCH, furan ring), 21.4 (CH3), 13.2 (CH3).
a
(deg)
b (deg)
c
(deg)
Z
Dcalculated (g cmꢂ3
F(000)
)
1.305
512
0.089
l
Mo K
a
(mmꢂ1
)
T (K)
230(2)
k (Å)
0.71073
0.089
None
ꢂ7/12, ꢂ13/14, ꢂ11/15
2.05/26.42
0.0403
Absorption coefficient (mmꢂ1
Absorption correction
Range of h, k, l
)
h min/max (deg)
R (int)
2.2. Crystallographic analysis
Completeness to theta = 26.42
Reflections collected/unique/
Data/restraints/parameters
GOF on F2
96.5%
7164/4907
4907/0/337
0.902
X-ray single crystal data were collected at 230 K using graphite
monochromated Mo Ka k = 0.7107 Å radiation on a Bruker SMART
APEX CCD diffractometer. Data reduction was carried out using
SAINT [19] and the structure was solved using SHELXS-97 [20]
and showed that there are two molecules of the title compound
in the form of a dimer in the asymmetric unit. Full matrix
refinement on F2 was performed with SHELXL-97 [20] and all
Final R indices [I > 2
R indices (all data) R1, wR2
r
(I)]R1, wR2
0.0466, 0.1131
0.0732, 0.1210
ꢂ0.241 eÅꢂ3, 0.211 eÅꢂ3, 0.05
337
D
qmin, Dqmax, Dqrms
Refinement number of parameters
Refinement number of reflections
4907

R.Y. Morjan et al. / Journal of Molecular Structure 1051 (2013) 345–353
347
and C16AC8AN2AN1. Besides, the furan moieties are found
slightly deviate from planarity with each other, with
4. Results and discussion
a
C2AO1AC16AO3 torsion of 5.8°. The phenyl moieties are in anti
orientation with each other, (C9AC13AC27AC23 torsion angle of
80.5°), adopting the well-known dorsal geometry with the
N2AC6AC8AC9 and N4AC20AC22AC27 torsional planes of 28.9°
for each with the hydrazone moieties.
4.1. Molecular structures
Preparation of the novel product (E)-N0-(1-p-tolylethylid-
ene)furan-2-carbohydrazide 3 in its dimeric form; hydrogen com-
plex adduct 4, was effected through a condensation reaction of
furan-2-carbohydrazide 1 and 1-p-tolylethanone 2 (Scheme 1).
The formation of 3 was confirmed by spectral data (1H NMR, 13C
NMR, FTIR, MS) and X-ray crystallography.
4.2. Geometrical Isomers
The 3D molecular structure of 4 is depicted in Fig. 1a and b; 1a
represents the experimental X-ray crystal structure with the num-
bering scheme while 1b displays the optimized DFT(B3LYP)/
6311+G(d,p) geometrical structure. Fig. 2 displays the orientation
of the two molecules of 3 (the dimeric form 4) in the asymmetric
unit of X-ray crystal viewed along the c-axis, where the red dotted
lines represent the hydrogen bonds.
Selected geometrical parameters; bond lengths and bending an-
gles, for 4 optimized as described above along with their experi-
mental counterparts are tabulated in Table 2. Our calculations
showed that both B3LYP and HF results are in good agreement with
their X-ray counterparts. This should validate our choice of level of
theory employed in this study of investigating such compounds.
Evidently, computed bond distances and bond angles are nicely
correlated with their experimental counterparts with regression
factors (R2) of (0.9928, 0.9685) and (0.9907, 0.9858) for DFT and
HF respectively. The DFT correlations are depicted graphically
and shown in (Fig. 3a and b).
The DFT/B3LYP results are in better agreement with the exper-
imental ones than those obtained by the HF level. Therefore, and
considering that the DFT/B3LYP satisfactorily takes into account
electron correlation contributions which are essential to investi-
gate highly conjugated and systems of lone electron pairs, the
DFT/B3LYP method was further employed in this study [31].
In 4, the experimental bond distances of N2AC6 and N4AC20
are equal to 128.4(2), 128.3(2). The corresponding B3LYP and HF
values are (129 pm, 129 pm) and (126 pm, 126 pm), respectively,
clearly, indicating the double bond nature of the two bonds. The
N1AN2 bond length is 137.5(19) pm, 136.4 pm and 135.8 pm as
it is predicted by X-ray, DFT and HF, respectively, while the
N3AN4 bond distance is found 137.9(2) pm, 136.4 pm and
135.8 pm by the same aforementioned experimental and theoreti-
cal methods, respectively. These data suggest a single bond be-
tween the nitrogen atoms. Theoretical calculations showed that
the hydrogen atoms H1 and H3 were equidistant to each of N1
and N3 atoms (102.9 pm and 100.4 pm by the DFT and HF, respec-
tively), while the corresponding X-ray distances are 90.5(19) pm
and 91.5(17) pm.
Due to the double bond geometry and the restricted rotation
around the N2@C6 bond, compound 3 was expected to exhibit E/
Z-stereoisomerism, and the synthesis might lead to form therefore
of both isomers. However, only the E-form around N2@C6 and thus
its dimeric E/E adduct were obtained. Accordingly, calculations on
the hypothetical Z/Z-adduct in addition to the Z-rotamer and the E/
Z-rotational transition structures at the same level of theory
DFT(B3LYP)/6-311+G(d,p) were performed.
Figures and Cartesian coordinates of both the Z-isomer and the
rotational transition structure around N2@C6 double bond at the
B3LYP/6-311+G(d,p) level of theory are reported in supplementary
materials, Figs. S1 and S2, respectively. The most important feature
of the rotational transition structure is the perfect planarity of
C6AN2AN1 moiety (180.0°) and the presence of one imaginary
symmetrical bending vibrational mode at
m
= ꢂ385.7 cmꢂ1 cen-
tered at N2 atom. In addition, the calculated bond distances
N1AN2 and N2AC6 are 129.3 pm and 126.3 pm respectively, i.e.
about 7.1 pm and 2.7 pm shorter than the DFT/B3LYP-based
lengths of the corresponding bond distances in the E-rotamer (E/
E-dimer). The DFT calculations showed that the hydrazone and
furanyl moieties in the Z/Z-dimer are in perfect planarity while
the phenyl moieties are parallel to each other, adopting anti
orientation with the skeleton of the Z-rotamer that constitute the
Z/Z-adduct. In a similar manner to the hydrazone moieties in the
E-rotamer and thus its E/E-adduct, the geometrical parameters of
the Z-rotamer and thus its Z/Z-adduct showed that the hydrazone
moieties between C8 and O2 and between C22 and O4 are
effectively planar but atoms are in cis-position in each of the two
constituent parts. One last thing is worth indicating here is that
the bond lengths of N1AC5 and N3AC19 in all geometries involved
in the study are shorter than the typical NAC single bond and
longer than a typical N@C bond, revealing the presence of the
hyperconjucation in the hydrazone moieties.
4.3. Energy calculations
Energies of the E/Z-geometrical isomers, E/E-dimer, Z/Z-dimer,
frontier orbitals and their dipole moments are listed in Table 3.
Our calculations predict that target compound 3 and its Z-rotamer
are ground states where the E-form is the global minimum on the
potential energy surface (PES). Evidently, the total energy of each
isomer is lower than the energy sum of its constituent monomers.
Geometrical parameters showed that the hydrazone moieties
between C8 and O2 and between C22 and O4 are effectively planar
and atoms are in trans-position in each of the two parts. Furan
rings of the dimer are slightly twisted away from the hydrazone
plans, forming a torsional planes 10.9° for each C2AC1AN1AN2
The energy difference (D
e) in kcal molꢂ1 between the two isomers
Scheme 1. Synthesis of (E)-N0-(1-p-tolylethylidene)furan-2-carbohydrazide.

348
R.Y. Morjan et al. / Journal of Molecular Structure 1051 (2013) 345–353
Fig. 1. (a) The experimental geometric structure of the title compound at the unit cell in its dimeric form, (b) the theoretical geometrical structure, Mullikan charges (red
color) and the hydrogen bonds in pm as predicted by B3LYP/6-311+G(d,p) level of theory. (For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
indicates that the Z-form is less stable than the E-form by
1.19 kcal molꢂ1. In the case of the dimers, the energy difference be-
tween the E/E-dimer and the Z/Z-dimer is remarkably enhanced to
E/Z rotamers. In subsequent calculations, the computed energies
were corrected to zero-point energy calculations. Transition struc-
ture was tackled using quadratic synchronous transit (QST2) with
the same B3LYP/6-311++G(2df,pd)//B3LYP/6-311+G(d,p) level of
theories. The stationary point was verified as first order saddle
point, and thus the energy barrier between the E/Z-geometrical
isomers was calculated. Which Minima does the transition struc-
ture connect has been identified by means of internal reaction
coordinate (IRC) with a maximum number of 30 points on each
7.66 kcal molꢂ1
.
The energy barrier between E/Z-geometrical isomers (
Deb) is
estimated as the energy difference between eisomer and eTS. Accord-
ingly,
D ,
eb between E-isomer and TS measures 34.16 kcal molꢂ1
while its value is 32.97 kcal molꢂ1 in the case of the Z-isomer,
and thus a net energy difference of 1.19 kcal molꢂ1 between the

R.Y. Morjan et al. / Journal of Molecular Structure 1051 (2013) 345–353
349
Fig. 2. Crystal packing (E)-N0-(1-p-tolylethylidene)furan-2-carbohydrazide viewed along the a-axis showing the pairwise intermolecular NAHꢁ ꢁ ꢁO hydrogen bondings in red
colors. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Table 2
Selected experimental and computed bond distances (pm) and bond angles (°) of the E/E-dimer of (E)-N0-(1-p-tolylethylidene)furan-2-carbohydrazide at B3LYP/6-311+G(d,p) and
HF/6-311+G(d,p) levels of theories.
Bond
Bond Distance/pm
X-ray
Angle
Bond angle/°
B3LYP
HF
X-ray
B3LYP
HF
C5AN1
C5AO2
C5AC1
C1AC2
C1AO1
O1AC4
C3AC2
N1AN2
N2AC6
C6AC7
C6AC8
C8AC13
C13AC12
C8AC9
C9AC10
C11AC14
O3AC18
O3AC15
C15AC16
C16AC17
C15AC19
C19AO4
C19AN3
N3AN4
N4AC20
C20AC21
C2OAC22
C22AC23
C25AC28
C22AC27
N3AH(3N)
N1AH(1N)
H(3N)ꢁ ꢁ ꢁO2
H(1N)ꢁ ꢁ ꢁO4
N1ꢁ ꢁ ꢁO4
N3ꢁ ꢁ ꢁO2
135.2(2)
123.1(19)
147(2)
134.2(2)
136.8(19)
135(2)
136.6
123.5
147.4
137.2
137.2
134.9
142.5
136.4
129
150.9
148.5
140.1
139.3
140.5
138.8
150.9
134.9
137.2
137.2
142.5
147.3
123.5
136.9
136.4
129
150.9
148.5
140.1
150.8
140.5
102.9
102.9
191.6
191.6
293.7
293.7
135
C5AN1AN2
121.4(15)
114(11)
124.5(11)
117.8(14)
109(15)
137.9(16)
113.0(14)
107.1(15)
126.4
122.1
114.3
123.3
119.1
109.2
137
113.1
107
125.4
125.4
106
110.8
119.7
120.3
120
115.7
124.1
120.2
111
117.7
121.6
120.2
121.4
121
122.3
114.9
122.4
119.3
109.7
136.6
113.7
106.1
126.2
127.7
105.3
111.2
120
119.6
120.3
115.9
124.3
119.8
110.9
118
121.4
119.9
121.5
120.8
120.9
107.7
122.3
114.9
122.5
119.3
109.7
136.6
113.7
106.1
168.8
168.8
120.6
148.3
134.9
135
132.7
143.3
135.8
126
151.1
149.4
138.8
138.7
139.3
138.1
151
C5AN1AH1N
N2AN1AH1N
C6AN2AN1
C2AC1AO1
C2AC1AC5
O1AC1AC5
C1AC2AC3
C1AC2AH2
C3AC2AH2
C4AC3AC2
C3AC4AO1
O2AC5AN1
O2AC5AC1
N1AC5AC1
N2AC6AC8
N2AC6AC7
C8AC6AC7
141.3(3)
137.5(19)
128.4(2)
148.8(2)
147.8(2)
139.1(2)
137.8(2)
139.3(2)
137.5(2)
151.1(2)
134.9(2)
137.1(2)
137.2(2)
140.4(3)
146.9(2)
122.9(19)
135.1(2)
137.9(2)
128.3(2)
148.9(2)
148.3(2)
139.1(2)
150.5(2)
138.5(2)
91.5(17)
90.5(19)
202.7(18)
208.7(19)
298.8(2)
292.4(2)
126.4
106.3(16)
111.1(16)
120.0(16)
120.4(15)
119.6(15)
116.0(15)
124.3(15)
119.7(15)
109.5
132.7
135
134.9
143.3
148.3
120.6
135
135.8
126
151.1
149.4
138.8
151
139.3
100.4
100.4
204.4
204.4
303.6
303.5
C6AC7AH7
C13AC8AC9
C13AC8AC6
C10AC9AH9
C12AC11AC14
C10AC11AC14
C12AC13AC8
C18AO3ACA15
C19AN3AN4
C19AN3AH(3N)
N4AN3AH(3N)
C20AN4AN3
C16AC15AO3
C16AC15AC19
O3AC15AC19
C15AC16AC17
N1AH(1N)ꢁ ꢁ ꢁO(4)
N3AH(3N)ꢁ ꢁ ꢁO(2)
117.1(16)
121.7(16)
119.5
121.3(2)
121.6(2)
121.2(18)
106.3(14)
120.4(15)
116.4(10)
123.1(10)
118.4(15)
109.1(16)
137.4(16)
113.1(15)
106.8(16)
174.2(16)
166.3(15)
121
107.3
120.1
116.3
123.3
119.6
109.2
137
112.7
106.7
170.7
170.7
side of the path and step size 0.3 amuꢂ0.5 bohr between points
where geometries were optimized at each point along the reaction
path. Fig. 4 roughly depicts the DFT/B3LYP estimated energy profile
of the E/Z-isomers and the transition state between them.
reactivity of the system [32]. The single crystal X-ray structure of
3 reveals the pairwise NAHꢁ ꢁ ꢁO intermolecular H-bonding (IHB)
interactions between two molecules as it is already illustrated in
Fig. 1(a) and (b).
The experimentally determined Hꢁ ꢁ ꢁO distances in the
N1AH1ꢁ ꢁ ꢁO4 and N3AH3ꢁ ꢁ ꢁO2 moieties are 208.7(19) and 202.7
(18) pm, respectively, slightly longer than the DFT (191.6 pm)
and HF (204.4 pm) computed values at the given basis set (Table 2).
Obviously, both the experimental and computed distances of the
4.4. Hydrogen bonding
Intermolecular and intramolecular H-bonding plays a crucial
role in determining molecular shapes, properties/functions, and

350
R.Y. Morjan et al. / Journal of Molecular Structure 1051 (2013) 345–353
B3LYP/6-311+g(d,p) R2=0.9928
210
190
170
150
130
110
90
(a)
(b)
80
100
120
140
160
180
200
220
Experimental Bond Lengths (Ao)
B3LYP/6-311+g(d,p) R2=0.9907
140
130
120
110
100
Fig. 4. Energy profile of E/Z-geometrical isomers predicted by B3LYP/6-311+G(d,p).
P
ꢀ
ꢁ
eadduct
ꢂ
iemonomer
D
eHB
¼
ð1Þ
n
Similarly, calculations on the hypothetical Z-rotamer and its Z/
Z-adduct at the same level of theory DFT(B3LYP)/6-311+G(d,p)
were then performed. Calculations showed that the Hꢁ ꢁ ꢁO distance
in each the N1AH(1N)ꢁ ꢁ ꢁO4 and N3AH(3N)ꢁ ꢁ ꢁO2 H-bonds is
191.9 pm, indicating that the HB-distance in the Z/Z-form is
0.3 pm longer than its corresponding DFT(B3LYP) value in the E/
E-form. Fig. 5 displays the molecular structure of the Z/Z-dimer
where the pairwise hydrogen bonds and the selected atomic
charges are given in red colors.
105
112
119
126
133
140
Experimental Bond Angles (o)
Fig. 3. (a) Correlation graphs of the calculated DFT and experimental molecular
bond distances of the title compound. (b) Correlation graphs of calculated DFT and
experimental molecular bond angles of the title compound.
Table 3
Energy calculations predicted that
DeHB of the Z/Z-dimer is
Total energy (e + ZPE); Energy of frontier orbital’s (eHOMO, eLUMO), electric dipole
moment (l), of E/Z-geometrical isomers of the targeted compound and their
transition state (TS) calculated at the B3LYP/6-311++G(2df,pd)//B3LYP/6-311+G(d,p)
3.33 kcal molꢂ1, revealing a stabilization energy of 6.66 kcal molꢂ1
.
Accordingly, the hydrogen bond stabilization energy factor stabi-
lized the E/E-dimer by 5.27 kcal molꢂ1 more than its stabilization
energy of the Z/Z-dimer. This finding is practically means that each
single one of the H-bonding of E/E-dimer is more stable than that
of the Z/Z-complex by 2.64 kcal molꢂ1. Since the energy difference
level of theory.
Isomer
e + ZPE(hartree)
eHOMO ðeVÞ
eLUMO ðeVÞ
l(D)
E
TS
Z
ꢂ801.845974
ꢂ801.791531
ꢂ801.844073
ꢂ1603.710958
ꢂ1603.698753
ꢂ6.2110
ꢂ6.0859
ꢂ6.4235
ꢂ6.0856
ꢂ6.0407
ꢂ1.7462
ꢂ1.8670
ꢂ1.4553
ꢂ1.8281
ꢂ1.3734
4.9998
3.9198
4.8302
0.0552
0.0001
(stabilization energy) between the two adducts is 7.66 kcal molꢂ1
,
E/E-Adduct
Z/Z-Adduct
all other probable factors contribution in stabilizing the E/E-adduct
over the Z/Z-adduct is 2.39 kcal molꢂ1. This implies that the hydro-
gen bonds play a crucial role in the stability of such stereoisomer-ad-
ducts. Therefore, one could rationalize that the stereo-selectivity of
the reaction and thus the formation of E-rotamer and its dimeric-ad-
duct rather than the Z-rotamer and its dimeric-adduct in the crystal
structure is basically referred to hydrogen-bonding stabilization en-
ergy. This result is in great consistent with literature where the
intermolecular NAHꢁ ꢁ ꢁO and NAHꢁ ꢁ ꢁN hydrogen bonds in E-acyl-
hydrazone compounds stabilized the crystal structure whether the
hydrogen bonds occur in a repeating unit to form a polymer or in a
self-dimer complex as our E-dimer [41–45]. Nevertheless, the
hydrogen bond geometrical parameters; DAH, DAHꢁ ꢁ ꢁA and
DAHAA (NAH, NAHꢁ ꢁ ꢁO, and NAHAO, respectively) of our complex
are slightly differ from those predicted by others, most probably, due
to the type of bonding among hydrazone moieties to form a dimer
rather than a polymer in the crystal lattice in addition to the influ-
ence of the attached substituent to the N@C moiety.
Mullikan distribution charges (Figs. 1b and 5) provide reason-
able explanation regarding the relative weakness of the Z/Z-dimer
hydrogen bonds. For instance the charges on N1, H1 and O4 are
ꢂ0.270, 0.414 and ꢂ0.22, respectively, in the Z/Z-dimer (Fig. 5),
while the corresponding charges on H, N and O atoms in the E/E-di-
mer (Fig. 1b) are ꢂ0.134, 0.419 and ꢂ0.289, respectively. As a nat-
ural result of this variety of N, H and O charges, a stronger N1ꢁ ꢁ ꢁH1
bonding interaction in the Z/Z-dimer on the expense of the O4ꢁ ꢁ ꢁH1
H-bonds in the dimeric form are significantly shorter than the van
der Waals radius of the Oꢁ ꢁ ꢁH bond (290 pm), but they are still
longer than a typical OAH covalent distance or the sum of their
covalent radii of about 130 pm [33]. The calculated NAHAO angles
associated with the H-bonds, N1AH1ꢁ ꢁ ꢁO4 and N3AH3ꢁ ꢁ ꢁO2 were
found to be slightly less than 180° and are in very good agreement
with their observed counterparts (Table 2).
H-bond’s energy, which can easily be attained by both experi-
mental (vibrational spectroscopic [26,34], X-ray crystallographic
[35–37] and Neutron diffraction [38,39] methods) and computa-
tional approaches, is well accepted measurable quantity employed
to describe the strength of the bond.
DeHB, the change in energy
associated with the formation of IHB, is evaluated using equation
1 as the energy difference between the HB complex and its constit-
uent molecules, where n is the number of hydrogen bonds exist in
the dimer, eadduct is the electronic energy of the dimer and emonomer
is the electronic energy of our respective molecule [40]. In our
work, both emonomer and eadduct were computed at B3LYP/
6-311++g(2df,pd)//B3LYP/6-311+G(d,p), and then corrected to
zero-point vibrational energies. The computed energies predicted
H-bond energy of 5.96 kcal molꢂ1
, giving rise to an adduct
stabilization energy due to hydrogen bonding by 11.93 kcal molꢂ1
compared to our targeted molecule.

R.Y. Morjan et al. / Journal of Molecular Structure 1051 (2013) 345–353
351
Fig. 5. Theoretical geometrical structure of the Z/Z-dimer, Mullikan charges (red color) and hydrogen bonds (blue color) in pm as predicted by B3LYP/6-311+G(d,p) level of
theory. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
hydrogen bonding would be resulted, and thus a weaker HB inter-
action in the Z/Z-dimer than what is observed in case of the E/E-
dimer.
modes involved in calculations, or in general, the number of times
the calculations are made [46,47].
!
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
ꢂ
N
X
1
N
theoritical value ꢂ experimental value
Relative deviation ¼
4.5. Harmonic frequencies
experimental value
i¼1
ð2Þ
Based on optimized geometries, the vibrational modes of fre-
quency of the targeted compound 3 and its dimeric form 4 were
computed at the B3LYP and HF level of theories at the assigned ba-
sis set and then compared to their corresponding observed FTIR
values. Each of the included structures has proved to be minimum
on the PES due to inexistence of any imaginary vibrational modes
in the calculated IR spectra of each of the investigated structures.
The most characteristic vibrational bands (observed and com-
puted) that have been selected for both the E-monomer and its di-
meric form along with their calculated relative intensities are
listed in Table 4. The vibrational bands assignments were accom-
plished by using Gauss-View molecular visualization program.
The vibrational modes of frequencies predicted by the DFT/B3LYP
level of theory of the dimer are in better agreement with the exper-
imental values (R2 = 0.9991) than those have been predicted of the
E-monomer (R2 = 0.9086). This result is in complete accordance
with the X-ray finding that the dimeric form of the titled com-
pound is the one that is predominant in the solid state rather than
the monomeric form. The relative deviation of the values predicted
for the E/E-dimer is 0.74% while it is 1.31% in the case of the
E-monomer. The vibrational modes predicted by the HF/6-
311+G(d,p) level of theory and scaled by 0.905 are either overesti-
mate or lower estimate the corresponding observed FT-IR values,
reporting a relative deviation of 2.09%. Relative deviation is usually
calculated using Eq. (2) where N is the number of vibrational
As it is clear from Table 4 that the DFT computed NAH stretch-
ing band of the dimeric form (
= 3183.2 cmꢂ1) is considerably
lowered than that of the monomer (
= 3387.0 cmꢂ1) calculated
at the same level of theory, but in pretty good agreement with
m
m
the FTIR finding (m
= 3178.0 cmꢂ1). The difference between the
two calculated values (203.8 cmꢂ1) could be attributed here to
the impact of the NAHꢁ ꢁ ꢁO intermolecular hydrogen bonding.
The electrostatic Hꢁ ꢁ ꢁO interaction weakened the NAH bond due
to electronegativity difference where oxygen atom is more electro-
negative than nitrogen atom.
The C@O band of the E/E-dimer appeared at
12.8 cmꢂ1 lower than the corresponding observed value and
25.5 cmꢂ1 lower than that of the monomer ( = 1670.8 cmꢂ1). This
m ,
= 1645.6 cmꢂ1
m
behavior could be referred to the dimerization that resulted as a conse-
quence of IHB. The dimerization weakened the C@O bond, lowering the
stretching force constant, which in turn negatively influenced the sym-
metrical stretching frequency of the carbonyl bond.
It is observed that the rocking (in-plane) and the wagging (out-
of-plane) bending bands have not been significantly influenced,
since the rocking and wagging bands of both the title compound
and its dimeric form are, nearly, equal. One of the most character-
istic bending bands is the strong band; out-of-plane bending, that
appears at 809.2 cmꢂ1 (in case of E-monomer) and 819.6 cmꢂ1 (in
case of the E/E-dimer) due to para-substitution in the phenyl

352
R.Y. Morjan et al. / Journal of Molecular Structure 1051 (2013) 345–353
Table 4
Comparison of the selected observed and the scaled calculated vibrational spectra and their intensities (Inten, km molꢂ1) of (E)-N’-(1-p-tolylethylidene)furan-2-carbohydrazide
and its dimeric form at the given level of theories.
Assignments of the selected bands
B3LYP/6-311+G(d,p)
Monomer
HF/6-311+G(d,p)
FT-IR
(cmꢂ1
)
Dimer
m
Inten
m
Inten
m
Inten
(cmꢂ1
)
km molꢂ1
(cmꢂ1
)
km molꢂ1
(cmꢂ1
)
km molꢂ1
m
m
m
m
m
m
m
m
m
m
m
m
m
m
(N1AH, N3AH) sym. str.
(C2AH) sym. str.
(Furan ring C3AH, C4AH) sym. str.
(Furan ring C3AH, C4AH) asym. str.
(C12AH12, C13AH13) sym. str.
(C9AH9, C10AH10) asym. str.
3387.0 18.96
3119.9 1.79
3147.2 0.10
3119.9 1.79
3073.3 16.09
3037.0 14.57
3059.4 2.66
3022.0 9.59
2954.4 16.84
2905.1 34.64
2897.3 10.37
1659.8 581.27
1592.3 19.80
3182.2 1887.3
3169.6 10.0
3145.8 0.26
3119.1 5.01
3350.1 984.51
3136.5 3.12
3104.7 0.84
3076.9 0.41
3040.2 4.40
3016.1 16.51
3005.2 17.25
3008.8 37.45
2882.9 23.94
2864.0 55.41
2881.9 5.59
1692.0 2303.31
1631.3 10.85
1716.7 362.70
3178.0 vs
3175.0 m
3175.0 w
3125.0 w
3085.0 m
3080.0 w
3075.4 w
2985.0 m
2985.0 m
2910.0 m
2911.6 w
1658.4 vs
1561.3 s
1561.3 s
3080.0
12.15
3075.0 2.91
3073.5 12.15
2974.5 9.51
2953.9 20.64
2903.6 74.46
2917.3 6.36
1627.6 2308.0
1594.1 10.27
1595.8 35.73
(C9AH9, C10AH10) sym. str.
(C7AH7a, C7AH7b, C7AH7c) asym. str.
(C14AH14a, C14AH14b, C14AH14c) asym. str.
(C14AH14a, C14AH14b, C14AH14c) sym. str.
(C7AH7a, C7AH7b, C7AH7c) sym. str.
(C@O) sym. str. +
q (NAH) rock
(Ph ring C@C) sym. str. + b (Ph ring CAH) bend
(C6@N2)sym. str. + m (Ph ring C@C) asym. str. + b (Ph ring CAH) bend + b (NAH) 1572.9 1.51
bend
m
m
q
q
q
m
(Furan ring C@C) asym. str. + b (Furan ring CAH) bend
(Ph ring C@C) asym. str. + b (Ph ring CAH) bend
(N1AH, N3AH) rock.
(Ph ring C9AH, C10AH, C12AH, C13AH) rock.
(N1AH, N3AH) rock.
(Furan ring C@C) sym. str.
(HAC4@C3AH), q (HAC17@C18AH) rock.
1539.2 44.03
1526.9 1.73
1560.0 114.6
1537.1 10.27
1632.4 2308.0
1510.5 85.5
1472.9 2.18
1451.0 311.31
1373.2 310.17
1358.9 0.16
1360.2 36.39
1337.0 386.49
1589.5 142.45
1579.5 5.90
1527.6 89.44
1511.8 14.89
1462.6 506.77
1441.6 311.90
1369.9 0.03
1361.6 0.25
1385.4 28.43
1361.2 506.77
1561.3 s
1507.0 m
1658.0 vs
1561.2 s
1491.2 w
1474.7 s
1383.2 s
1370.0 w
1367.9 s
1303.1 s
–
–
1486.3 8.27
1455.2 6.81
1434.6 108.16
1367.2 71.33
1359.3 0.34
1350.6 17.92
1311.5 288.00
q
b(C14AH14a, C14AH14b, C14AH14c) bend
b(C7AH7a, C7AH7b, C7AH7c) bend.
m
(C5AN1) sym. str. +
(NAH) bend
m
(Furan ring C2AC3) str. + b (Furan ring CAH) bend + b
q
m
m
(HAC9AC10AH),
(C6AC8, C20AC22) sym. str.
(C25AC28, C11AC14) sym. str.
(Furan ring C4AH, C3AH, C2AH) rock.
q
(HAC23AC24AH) rock.
1286.2 4.30
1263.9 130.95
1184.8 2.16
1197.2 4.09
1163.2 3.38
1158.2 63.96
1131.6 196.80
1286.9 7.46
1263.9 159.68
1223.0 0.57
1223.0 6.83
1203.0 0.23
1158.7 84.07
1129.4 234.18
1308.4 0.78
1281.4 0.53
1189.6 60.98
1228.0 0.03
1195.2 26.62
1180.3 1.29
1137.5 3.78
1122.4 101.81
1299.5 w
1270.0 s
1218.0 w
1210.0 w
1183.8 w
1134.0 s
1134.0 s
1076.3 m
q
f (Ph ring C9AH, C10AH) sciss.
m
m
m
(Furan ring CAO) asym. str. + b (Furan ring C4AH) bend
(NAN) sym. str. + b (NAH) bend + b (Furan ring C4AH) bend
(Furan ring CAO) sym. str. + b (Furan ring C4AH) bend +
C9AH) bend
m
(NAN) s + b (Ph ring 1106.8 56.79
1109
25.05
x
x
s
x
x
(Ph ring CAH) wag
(N1AH, N3AH) wag
(N1AH, N3AH) twist.
(C4AH + C3AH + C2AH) wag.
(N1AH, N3AH) wag.
809.2
–
–
742.0
735.8
38.79
–
–
73.08
13.84
819.6
779.5
755.4
740.9
726.6
49.03
118.7
1.39
78.02
2.31
833.7
767.9
744.7
734.7
705.9
49.58
98.68
1.08
2.07
6.43
881.6 m
817.3 m
758.2 s
758.2 s
716.1w
m
:stretching frequency, sym. str.: symmetrical stretching, asym. str.: asymmetrical stretching,
q: rocking, b:bending, f:scissoring,
s: twisting, x: wagging. The signs vs, s, m,
and w stand for very strong, strong, medium and weak band intensities, respectively.
moieties according to DFT calculations. The corresponding ob-
only. Our calculations showed that H-bonds of the E/E-adduct are
more stable than those of the Z/Z-adduct by 5.27 kcal molꢂ1, i.e.
the thermodynamic stability of E/E-dimer is implicitly explained.
served band appears at 818.8 cmꢂ1
.
In general, the stretching bands of both the (E)-N0-(1-p-tolyle-
thylidene)furan-2-carbohydrazide and its E/E-dimeric form are
varied irregularly with no obvious trend.
Acknowledgments
The authors would like to thank Deanship of Scientific Research
at the Islamic University of Gaza for their financial support to R.
Morjan and A. Awadallah.
5. Conclusion
(E)-N0-(1-p-tolylethylidene)furan-2-carbohydrazide has been
synthesized and characterized by means of FTIR, NMR, MS and sin-
gle crystal X-ray crystallography. It also was subjected to computa-
tional investigations utilizing both HF and DFT/B3LYP model with
6-311+G(d,p) as a basis set. The level of theories employed have
produced precise correlations with the experimental findings in
terms of geometrical and vibrational parameters. This verifies the
appropriateness of our choice of level of theories and the suitability
of the DFT/B3LYP in such calculations to a better extent than the HF
model. Hydrogen bonds and energy calculations have provided in-
sight on the reason behind the stereospecificity of the reaction;
production restriction on the E-rotamer and thus its E/E-adduct,
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.molstruc.
2013.08.008.
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